Enterics Flashcards
What defines enterics?
1) rod-shaped
2) gram-negative
3) occuring in the GI tract
4) facultative anaerobes
What are three main enteric bacteria?
1) Shigella
2) Salmonella
3) Escherichia
Which sites do enteric bacteria infect?
Any site!
What are some common community-acquired enteric infections?
enteritis or colitis. cystitis, pyelo
What does nosocomial infection mean?
infection originating in the hospital
What is a major nosocomial infection?
Opportunistic Klebsiella pneumoniae infection
What is the average size of bacteria of Enterobacteriaceae?
0.5-2.0 microns
How are Enterobacteriaceae microbes motile?
peritrichous flagella
What are the two non-motile species of Enterobacteriaceae?
1) Klebsiella
2) Shigella
What is the most common selective media for enterics?
MacConkey agar
What is an important distinction for selective isolation of enterics?
Lactose fermentation
How are Enterobacteriaceae species identified?
biochemical reactions
How are subtypes of Enterobacteriaceae bacteria identified?
serotyping of antigens
What are the three antigens of enterics?
O antigen
H antigen
K antigen
What is the O antigen?
O polysaccharide of LPS
What is the H antigen?
flagella
What is the K antigen?
capsule
What is the exception to K antigen?
Vi-antigen of Salmonella
Where can you find E.coli?
As part of the normal commensal flora of the Gi tract
How are E.coli turned into pathogens?
Through the uptake of pathoenicity-associated islands, phages, and plasmids
How have pathovars of E.coli evolved?
through HGT!
What is EHEC?
Enterohemorrhagic E.coli
What is the most abundant facultative anaerobe in the gut?
E. coli
What does EHEC produce?
hemorrhagic colitis
Why is the primary infection of EHEC not of real concern?
it is usually self-resolving and not fatal
What do 15% of EHEC infections evolve into?
hemolytic uremic syndrome
What can hemolytic uremic syndrome lead to?
CNS manifestations and acute renal failure
Where is the incidence of EHEC the greatest?
developed countries
Is O157:H7 the only serotype which causes hemorrhagic colitis?
no!
What is the primary reservoir of EHEC?
cattle
Is EHEC pathogenic in cattle?
no
How do you transmit EHEC?
fecal-oral route
What is the infectious dose of EHEC and what is significant about this?
10-100 bacteria, which is very low
Is stomach acid a strong barrier to intestinal infection?
Yes.
Can a lack of stomach acid lead to a higher susceptibility to infection?
Yes.
What is a pathogenic feature of EHEC?
A/E lesions
What are A/E lesions?
Attaching and effacing lesions. These are parts of the intestinal epithelium which the bacteria uses to inject in proteins and take over the cells
How does pathogenic E. coil promote diarrhea?
1) tight junction disruption
2) loss of absorptive surface area
What does Shiga toxin bind?
Gb3 receptors
Why is Shiga toxin called Shiga-like toxin in E.coli?
It shares similarity to Shiga toxin produced in virulent strains of Shigella
Which is the more potent of the Shiga-like toxins?
Stx-2
What encodes for Stx in E.coli?
lambda phage
Why is the treatment of EHEC with abx controversial?
Because it leads to larger release of Shiga toxin and thus worse symptoms.
Why are there systemic sequela from EHEC?
Stx binds globotriaosylceramide receptors which are prominent in the endothelium of the various organs, especially the kidneys
How does Shiga or Shiga-like toxin work?
deadenylates 60S rRNA subunit
What are the classic triad of symptoms of dysentery?
1) abdominal cramping
2) tenesmus
3) frequent, small-volume, bloody, mucoid discharge
What is tenesmus?
Urge to defecate without or without actual production of fecal matter
How do the strains of Shigella line up in terms of pathogenicity?
sonnei < flexneri «_space;dyseneteriae
What is the fatality rate in S. dyseneteriae epidemics?
5-15%
What is Shigella thought to be a pathovar of?
E.coli
What is the significance of fecal leukocytes?
invasive enteric pathogens provoke an inflammatory response resulting in high fecal leukocyte count
What are the predominant Shigella infections in the US?
S. sonnei
What is the primary reservoir for Shigella?
humans
What is the infectious dose for Shigella and is it high or low?
<200 bacteria, low!
What is the US incidence of Shigella infections?
~15k/year
What are the primary targets of Shigella infections?
1) travelers
2) children in day care
How many global infections of Shigella are there?
150 million per year
Which is the most common strain of Shigella in the world?
Flexneri
How does Shigella infect the intestines?
Phagocytosis by the M cell, and then makes its way to the basolateral membrane. It then replicates intracellularly and spreads through the actin cytoskeleton.
Which strain has Shiga toxin?
Shigella dysenteriae Type 1
What is the difference between EHEC and Shiga toxin in Shigella?
The gene for Shiga toxin in Shigella is in the bacterial genome rather than a phage
What differentiates Salmonella from the other Enterobacteriaceae species?
1) produces H2S
2) phase variably motile
Which types of infections are worse: broad host-range or narrow host-range?
Narrow host-range
What are the two clinical presentations of Salmonella infections?
1) gastroenteritis
2) Typhoid fever
